Composite electromagnetic wave absorber and method of fitting the same

Abstract

A composite electromagnetic wave absorber capable of restricting the height of a pyramidal electromagnetic wave absorber and being applied to a compact anechoic chamber, wherein an upper absorber (3) is fabricated by dispersing ferrite powder in a general-purpose resin having a permittivity of not higher than 4.9.

What is claimed is:  
     
       1. A composite electromagnetic wave absorber comprising an assembly fabricated by bonding ferrite tiles and upper absorbers having a shape of a flat plate, a wedge shape or a pyramidal shape, wherein said upper absorber is prepared by dispersing ferrite powder in a general-purpose resin having a permittivity of not greater than 4.9 at a frequency of at least 1 MHz, wherein said ferrite tile comprises Fe 2 O 3 , NiO, ZnO and CuO as the principal components, said ferrite powder in said upper absorber comprises Fe 2 O 3 , NiO and ZnO as the principal components, and said general-purpose resin comprises at least one non-polar resin or resin approximate to said non-polar resin selected from the group consisting of polyethylene, polypropylene, a fluorocarbon resin, polytetrafluoroethylene, an allyl resin, an epoxy resin, a vinyl chloride resin, a vinyl acetate resin, a styrol resin, an acrylic resin, a polyamide resin, a polyacetal resin, a polycarbonate resin and an acetyl cellulose resin. 
     
     
       2. A composite electromagnetic wave absorber according to  claim 1 , wherein said upper absorber contains, in terms of a volume fraction, 10 to 65 vol % of said ferrite powder and the balance comprising said general-purpose resin, and a ratio μr/εr of a permeability μr to a permittivity εr in a frequency range of not higher than 1 GHz satisfies the relation: 
       
         
           0.25≦μr/εr≦2.5.  
         
       
     
     
       3. A composite electromagnetic wave absorber according to  claim 2 , which satisfies the relation: 
       
         
           μr/εr=1.  
         
       
     
     
       4. A composite electromagnetic wave absorber according to  claim 1 , wherein said upper absorber contains, in terms of a volume fraction, 30 to 65 vol % of the ferrite powder and the balance comprising at least one kind of resins selected from polyethylene, polypropylene, a fluorocarbon resin and polytetrafluoroethylene; a ratio μr/εr of a specific permeability μr to a specific dielectric constant εr within a frequency range of not higher than 1 GHz satisfies the relation: 
       
         
           0.25≦μr/εr≦2.5;  
         
       
       and absorption performance within a frequency range of 100 MHz to 10 GHz is at least 20 dB. 
     
     
       5. A composite electromagnetic wave absorber according to  claim 4 , which satisfies the relation: 
       
         
           μr/εr=1.  
         
       
     
     
       6. An electromagnetic wave absorber panel having a pyramidal shape, comprising a resin and ferrite as principal components thereof, and being so arranged as to match material-wise with a spatial impedance, wherein said electromagnetic wave absorber panel has an integral panel shape of four interconnected face portions of a pyramid, and portions for screw fastening are shaped at the center and at four side edge portions of said panel. 
     
     
       7. A fitting method of an electromagnetic wave absorber panel, comprising: 
       providing an electromagnetic wave absorber panel comprising a resin and ferrite as principal components thereof, and being so arranged as to match material-wise with a spatial impedence, wherein said electromagnetic wave absorber panel has an integroal panel shape of four interconnected face portions of a pyramid, and a portion for screw fastening is formed at the center and at each of four side edge portions of said panel;  
       applying an adhesive to the bottom face of said panel;  
       fastening by a screw said electromagnetic wave absorber panel onto a shield panel comprising a plurality of ferrite tiles through a screw hole formed at the center of said electromagnetic wave absorber panel and a through-hole formed at the center of a ferrite tile of said plurality of ferrite tiles; and  
       fixing the side portions of said electromagnetic wave absorber panel using in common one screw through a screw hole formed from said portion for screw fastening formed at a side edge portion of said panel when said electromagnetic wave absorber panels are butted to one another, and through a through-hole at the center of another ferrite tile of said plurality of ferrite tiles.  
     
     
       8. A compact anechoic chamber for EMC evaluation, comprising: 
       a shield chamber having the outermost portion thereof constituted by a metallic plate or shield panels for constituting said metallic plate;  
       ferrite tiles fitted to the entire surface of said metallic plate or said shield panels; and  
       an electromagnetic wave absorber fitted to the entire surface of said ferrite tiles or to a part of the center of each surface, said electromagnetic wave absorber comprising an assembly fabricated by bonding ferrite tiles and upper absorbers having a shape of a flat plate, a wedge shape or a pyramidal shape, wherein said upper absorber is prepared by dispersing 30 to 65 vol % of ferrite powder in a general-purpose resin having a permittivity of not greater than 4.9 at a frequency of at least 1 MHz and selected from the group consisting of polyethylene, polypropylene, a fluorocarbon resin and polytetrafluoroethylene, wherein said ferrite tile comprises Fe 2 O 3 , NiO, ZnO and CuO as the principal components and said ferrite powder in said upperabsorber comprises Fe 2 O 3 , NiO and ZnO as the principal components, and wherein μratio  82  r/εr of a specific permeability μr to a specific dielectric constant εr within a frequency range of not higher than 1 GHz satisfies the relation:  
       
         
           0.25≦μr/εr≦2.5;  
         
       
       and an absorbtion performance within a frequency range of 100 MHz to 10 GHz is at least 20 dB.  
     
     
       9. A composite electromagnetic wave absorber comprising an assembly fabricated by bonding ferrite tiles and upper absorbers having a wedge shape or a pyramidal shape, wherein said upper absorber is prepared by dispersing ferrite powder in a general-purpose resin having a permittivity of not greater than 4.9 at a frequency of at least 1 MHz.